Shunt



Feb. 8, 1927. 1,617,145

c. G. BROWN SHUNT Filed Jan. 6, 1925 Fi .lf Fig.2. -Fig.3.

' H is AttOTT'! ey Patented Feb. 8, g I

UNITED STATES 1,617,145 PATENT OFFICE.

CARROIJ G. BROWN, OE SCHENEOTADY, NEW YORK, ASS IGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

snomr.

Application filed January 6, 19:25. Serial no. 900.

My invention relates to a variable ratio electric shunt suitable foruse in connection with an electric measuring instrument to determine voltage and current values.

In electrical current measurements, use is often times made of a sensitive galvanometer connected across a shunt so that only a small portion of the current to be measured passes through the galvanometer. In order that the combination may be used over a wide range of current values, the shunt may be provided with a number of contacts so arranged that by changing the contact connections, the ratio of the current flowing through the galvanometer tothe total current may be altered. In the variable ratio shunts known to the prior art a change in the shunt ratio changes the resistance of the combination. It is often times desirable to maintain the resistance of the shunt combination constant, for example where a shunt and alvanometer combination is used in the circuit of a thermocouple to measure temperatures or measurements responsive to temperature changes. In such a circuit, in order to take a reading on a iven shunt tap and interpret said reading y means of a calibration that was made while using a dif ferent tap, requires that the resistance of the circuit be maintained constant. Consequently, it would be very inconvenient to have the resistance ofthe circuit changed when changing the ratio of the shunt. It is the primary object of my invention toprovide a variable ratio shunt which has a constant resistance for all ratios.

lhe featlures'of my invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. For a better understanding of my invention reference is made in the following description to the accompanying drawing, in which Figs. 1 to 10 inclusive represent shunt combinations which will be referred to in the I development of the theory upon which my improved shunt is based, Fig. 11 represents a simplified connection diagram for an 8- shunt built in accordance with my invntion, and Fig. 12 represents a shunt having a different variation factor.

In orderto make this explanation as nontcchnical "as possible, the simplest case is used to :start with, and developed on up through to the final form of the shunt. For

the sake of simplicity. I will assume a galvanometer resistance of r in the following vanometer is indicated by G. Fig. 1 shows a resistance of Main parallel with the galvanometer. The combined resistance in this case 15 r l0r The total current I flowing in the circuit will divide up between the two-branches in inverse proportion to their respective resistances, that is, Ig, the galvanometer current, will be "1-? of I.

Fig. 2 is equivalent to Fig. 1, except that the shunt resistance is divided into two sectlons having resistances of 9rand r respectively.

Fig. 3 is the equivalent of, Fig. 2, except that a multiple tap switch S is provided whereby the left side of the line may be connected on either side of the 97* resistance section and is shown connected to a tap between the galvanometer G and the parallel connected resistance.

Fig. 4 shows the switch S on the other tap between the two resistance sections. The combined resistance has remained the same, s1nce we still have two branches in parallel of 101 and 1 respectively. In Fig. 4 however, the current ratio of the shunt has been reduced to of its previous value. That is to say, I9 is only T 1 of the total current I, or of its previous value.

For the resistance section of Fig. 4, we may substitute two parallel resistances of and 101' respectively, as represented in through the galvanometer. vThis latter cur- '110 rent lg is dependent upon the relative resistance ot the two branches, and is therefore by simple proportion equal to of I. As shown in connection with Fig. 5, a 107* 10 resistance and a 1' resistance 111 parallel may be substituted for resistance r without any change in the combined resistance; vice versa, in Fig. 8, we may substitute?" for these two parallel branches as represented in Fig. 9, which may befurther simplified as in Fig. 10, the proportionate value of I and 1 remaining the same.

Now l, or the total current, will divide up inversely proportional to the two branches here representedand therefore I will be of 1. Above it was shown that lg was equal to W of .l and therefore lg will be equal to if} of l which is of the value of Ig in the case of Fig. 4. Also, in-Fig. 10, the total combined resistance is the same as in Fig. 7, Fig. 5 and Fig. 3, or i gr.

lit has been shown above tor three points, that with the switch at any point, the total combined galvanometer and shunt IBSlSl): ance is the same. It has also been showr that the current ratio is diminished by a otactor at 10 for each successive point, since the galvanometer current had successive values of and of the-total current. The same line of reasoning may be used for any number of points and the same conditions will hold.

In Fig. 11 I have shown a shunt designed in accordance with my invention having 8 points. By progressively applying the formules for parallel connected resistances the average galvanometer such for example as 100 ohms.

It will be noted that in any one shunt but three values of resistance are used r, 91 and 101' Having a number of resistance elements all alike in itself makes for lower cost of building and maintaining such a shunt.

Besides this, all three values of the resistances used are not of widely different values as in multiple point shunts heretofore used. This permits of building a shunt with any number of points desired. Due to the fact that'the combined resistance of the circrut site resistanceratios for constant resistance on all taps where the tap ratio is 5. In this case the combined resistance is in all cases and the Ig is for the upper tap .5 for the middle tap and for the lower From the above it will be seen that the improved shunt has certain definite resistance and. ratio relations which may be expressed as follows: If we let 1' equal the resistance I of the galvanometer and w the ratio factor between consecutive taps, which factor is 10 in Fig. 11 and 5in Fig. 12, then we ma say that the constant resistance relation M i hold when the parallel resistance connected between the highest ratio tap and the opposite side or" the line is r, the other parallel connected resistances are and the resistance between (a -Ur.

In the foregoing I have specified a galvanometer as the device used 'in combination with the shunt but this device might be any other current consuming device or apparatus of constant resistance in which it is desired to vary the current while maintaining the combined resistance of the circuit constant.

In accordance with the provisions of the Patent Statutes, I have described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown and described in only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A constant resistance variable ratio shuntand galvanometer combination comprising a galvanometer having a resistance of r, a plurality of parallel resistance sectaps are each tions, all connected at one end to one side of said galvanometer, and at the other end to a the parallel resistance sections except the one most remote from the galvanometer havmg a reslstance value equal to and the most remote parallel connected resistance being equal to that of the galvanonzeter, a: being any desired ratio factor.

2. A translating device having a resistance of 1" and a multiple ratio shunt therefor for varying the ratio of current flowing through said device comprising a plurality of parallel resistance sections having a common connection at one end to one side of said translating device and having taps at the other end, said taps being separated from each other by other resistances each having a value of (m--1)r, one of said taps being connected to the other side of said translating device by a resistance of (ac-Dr, all of the parallel resistance sections except the one most remotely connected with the translatmg device having resistance values of In witness whereof, I have hereunto set my hand this 5th day of January, 1925.

CARROL G. BROWN. 

